To be sure, other factors could have caused the system failures ahead of the March 26 crash, and the National Transportation Safety Board has said it’s just beginning its investigation. But the incident has in general focused attention on a little-known problem that falls into a gray area where oversight is limited and the purveyors of faulty fuel rarely face accountability, legal and maritime experts say.

“It’s an open secret that fuel contamination issues plague the industry with most of the incidents going unreported or not resulting in any substantial damage to the vessel or property or life,” said James Power, a New York maritime lawyer and former merchant marine and engineering officer on American ships.

Power has represented several ship owners whose vessels were damaged by contaminated fuel. The vast majority of such incidents don’t result in catastrophic harm to property or the vessel itself, he noted. 

“Those situations are rare, but are foreseeable results when an industry lacks self-regulating mechanisms to identify contaminated fuel before it is sold, put on board the vessel and consumed in the vessel’s engines,” Power said.

Fuel contamination not only puts ship crew members at risk, but also can cause pollution and damage the reputations of shipping companies, said Steve Bee, group commercial and business development director for VPS, a testing service that provides information to more than 12,000 vessels around the world and issues alerts on contaminated fuel. The Dali, he said, was not a client.

Contamination isn’t confined to any geographic region or supplier, Bee said: “It can happen anywhere, anytime.” 

He said VPS hadn’t issued any recent fuel contamination alerts in China or South Korea. 

A spokesman for the Danish shipping giant Maersk, which chartered the Dali, declined to comment on whether fuel may have been a factor in the accident.

“Regarding fueling, we are closely following the investigations conducted by authorities and the vessel operator as well as conducting our own investigation,” the spokesperson, Kevin Doell, said in an email. 

Synergy Marine Group, which operates and manages the ship, and Grace Ocean Private, which owns it, did not immediately respond to requests for comment. 

Jennifer Homendy, chair of the NTSB, said at a news conference Wednesday that investigators would take a sample of the fuel and test it for contaminants, as authorities work to determine the cause of the crash. 

The U.S. Coast Guard referred questions to the group of agencies handling the response to the crash, which did not respond.

Port officials in Zhangzhou and Zhoushan did not immediately respond to questions. 

Busan port authorities said they wouldn’t have information about issues with fuel. The Korea Coast Guard’s Southern Sea Division told NBC News it had received no reports of fueling-related incidents this year. 

The LRIT system that showed the Dali’s movements tracks all commercial vessels over 3,000 gross tons. The details on fuel delivery come from a report that is signed by both the delivery ship and the receiving ship, which goes to the government of the country where the transfer took place, as well as the flag state of the ship that received the fuel, and is then automatically added to the LRIT system.

A spokeswoman for the International Maritime Organization, the United Nations agency that regulates international shipping and runs the LRIT, declined to comment on specifics of the Dali investigation.

She said fuel oil quality is regulated under the International Convention for the Prevention of Pollution from Ships, also known as MARPOL, which states that fuel should not include harmful added substances or chemical waste. It also covers fuel oil sampling, she added. 

Member states are required to notify the International Maritime Organization of incidents, she said.

But the system has major gaps, experts say. 

“What constitutes an incident is murky,” said Jonathan Arneault, the CEO of FuelTrust, a Houston-based company that uses artificial intelligence to trace the provenance of marine fuel.

“It’s usually defined as harm or risk to safety or environment,” he said. “If the ship doesn’t meet that threshold, it’s not reported. So the member state has nothing to report.”

Arneault said the supply chain for ship fuel, also known as bunker fuel, is maddeningly opaque and few countries have strong laws on fuel management.

While water is a common contaminant in fuel, it is rarely enough to cause a major system failure. Heavier, more corrosive particulates are a more likely culprit, experts say.

Fuel contamination is often unintentional, but there have been cases of unscrupulous fuel providers diluting their product with cheaper substances to increase supply and maximize profits. 

“They can do a lot of weird things for money,” said Thomas Roth-Roffy, a former NTSB marine investigator who retired in 2016. 

But he said the power failure on the Dali could very well have had nothing to do with the fuel or fuel system. 

“As the diesel engine has hundreds of components subject to failure, there are many possible scenarios that could cause the engine to malfunction,” he said.

Arneault suspects that the Dali may have been running on fuel at the bottom of its tank — where a heavier contaminant would have settled — when the power went out. He believes the fuel is to blame because security video captured the lights on the Dali flicking off and on a couple of times, and black smoke billowing from its chimney, before the Singaporean vessel slammed into a bridge support.  

“It’s likely not just an engine problem because the generators go out,” Arneault said, noting that the generators likely would have been using the same fuel. “That indicates it’s probably a fuel issue.”

What caused the ship to lose power isn’t the only open question. According to some experts, the Dali would have needed more fuel to make it to Sri Lanka, its planned destination when it hit the Key Bridge, but the available tracking data does not confirm any fuel deliveries in New York or Baltimore.

When fuel is delivered to a ship, a sample is sent for lab testing before it is supposed to be used to fire an engine. However, those tests don’t examine all of the possible contaminants. Arneault said he thinks the tests should be expanded, but they are already costly and there is little enthusiasm among ship operators for such a change.

Although most incidents involving bad fuel go unreported, they do occasionally spark industry warnings, investigations and legal battles.

In 2018, about 200 ships were affected by fuel contaminated with a chemical used to make epoxy. Some experienced power loss. Testing companies traced the fuel to Houston, Panama and Singapore. Researchers said at the time that the contamination was a symptom of an opaque supply chain that allowed a “witch’s brew” of additives — a sign of a looming crisis. 

Four years later, in 2022, Singapore authorities reported an outbreak that affected nearly three dozen ships, 14 of which suffered loss of power and engine problems, according to researchers. An investigation later named two suppliers, one in Singapore and the other in China, as the source. One had its license suspended.

Last year, the U.S. Gulf Coast was stricken with contaminated fuel that disrupted the engines of 14 vessels, some of which lost power and propulsion while at sea. VPS traced the dirty fuel to Houston and Singapore.

Arneault said the contaminated fuel incidents that get media attention represent only a fraction of those that actually occur. He tallied more than 120 such cases last year and at least 460 in 2022 based on private incident databases and information he received from fleet managers. 

“For more than 50 years, people in the ship fuel market have tolerated small losses,” Arneault said, “or even small-scale fraud, thinking these issues were too minor to worry about. But the last five years have taught us that even these ‘minor’ problems can lead to huge risks and big costs.”